Philippa Kaur

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    in Space & Astronomy

    A newfound gravitational wave ‘hum’ may be from the universe’s biggest black holes

    Citations
    G. Agazie et al. The NANOGrav 15-Year data set: Detector characterization and noise budget. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acda88.G. Agazie et al. The NANOGrav 15-year data set: Evidence for a gravitational-wave background. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acdac6.G. Agazie et al. The NANOGrav 15-year data set: Observations and timing of 68 millisecond pulsars. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acda9a.A. Afzal et al. The NANOGrav 15-year data set: Search for signals from new physics. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acdc91G. Agazie et al. The NANOGrav 15-year data set: An astrophysical interpretation of a gravitational wave background from supermassive black hole binaries. Astrophysical Journal Letters. In press, 2023.J. Antoniadis et al. The second data release from the European Pulsar Timing Array I. The dataset and timing analysis. Astronomy & Astrophysics. Published online June 28, 2023.J. Antoniadis et al. The second data release from the European Pulsar Timing Array II. Customised pulsar noise models for spatially correlated gravitational waves. Astronomy & Astrophysics. Published online June 28, 2023.J. Antoniadis et al. The second data release from the European Pulsar Timing Array. III. Search for gravitational wave signals. Astronomy & Astrophysics. Published online June 28, 2023.A. Zic et al. The Parkes Pulsar Timing Array Third Data Release. Publications of the Astronomical Society of Australia. Published online June 28, 2023.D.J. Reardon et al. Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array. Astrophysical Journal Letters. Published online June 28, 2023. D.J. Reardon et al. The gravitational-wave background null hypothesis: Characterizing noise in millisecond pulsar observations with the Parkes Pulsar Timing Array. Astrophysical Journal Letters. Published online June 28, 2023.H. Xu et al. Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data Release I. Research in Astronomy and Astrophysics. Vol. 23, July 2023, p. 075024. doi: 10.1088/1674-4527/acdfa5. More

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    in Humans

    The myth that men hunt while women stay at home is entirely wrong

    A woman from the Dani tribe in Indonesia with a bow and arrowANDREY GUDKOV/Alamy
    The idea that men hunt while women stay at home is almost completely wrong, a review of foraging societies around the world has found. In fact, women hunt in 80 per cent of the societies looked at, and in a third of these societies women were found to hunt big game – animals heavier than 30 kilograms – as well as smaller animals.
    These findings are likely to be representative of all foraging societies past and present, says Cara Wall-Scheffler at the University of Washington in Seattle. “We have nearly 150 years of ethnographic studies sampled, we have every continent and more than one culture from every continent, and so I feel like we did get a pretty good swathe of what people do around the world,” she says.
    There was already growing evidence that women hunted in many cultures in the past. For instance, of 27 individuals found buried with hunting weapons in the Americas, nearly half were women, a 2020 study found. Yet researchers have been reluctant to conclude that these women were hunters.Advertisement
    “There is a paradigm that men are the hunters and women are not the hunters, and that paradigm colours how people interpret data,” says Wall-Scheffler. Her team looked at a database called D-PLACE that has records on more than 1400 human societies worldwide made over the past 150 years. There was data on hunting for 63 of the foraging societies recorded and, of these, 50 described women hunting.
    For 41 of these societies, there was information on whether women’s hunting was intentional or opportunistic – that is, whether they were going out to hunt rather than catching animals they stumbled upon while gathering plants, say. In 87 per cent of cases, it was intentional. “That number was higher than I expected,” says Wall-Scheffler.
    The team also looked at data on the size of animals hunted by women, which was recorded for 45 societies. In 46 per cent of cases it was small game such as lizards and rodents, 15 per cent medium game and 33 per cent large game. In 4 per cent of the societies women hunted game of all sizes.
    The analysis found that women’s hunting strategies were more flexible than men’s. “Women use a wider range of tools when they go hunting, they go out with a wider variety of people,” says Wall-Scheffler.

    They may hunt alone or with a male partner, other women, children or dogs, for instance, says Wall-Scheffler. While the bow and arrow was commonly used by female hunters around the world, she says, women also used knives, nets, spears, machetes, crossbows and more.
    This greater flexibility could be a result of female hunters’ mobility varying when they are pregnant or breast-feeding, she says. In at least some cases women hunted with babies strapped to their backs, for instance.
    In some societies there were taboos on women making or using specific tools or weapons, Wall-Scheffler says, forcing them to find alternatives.
    “This paper represents a much-needed meta-analysis,” says Randy Haas at Wayne State University in Michigan, whose team carried out the study of burials in the Americas. “The findings, coupled with related archaeological findings, convincingly show that division of subsistence labour is much more variable than previously thought,” he says.
    Given that women did and do hunt in so many societies, Wall-Scheffler says she can’t explain why the popular notion is that only men hunt. “I don’t understand it,” she says. “I think it is just as remarkable that women with babies on their back are going out to shoot animals.”

    Topics:women/hunting More

  • 150 Shares189 Views

    in Humans

    History reveals vital new lessons in how to make our societies better

    Bernard Friel/Education Images/Universal
    WHY is society the way it is? We thought we knew. Now, it appears, we have been thinking about it all wrong.
    In our special issue on civilisation (see The civilisation myth: How new discoveries are rewriting human history), we explore what has happened to human societies over the past 10,000 years and what came before. It details new evidence on why many of us abandoned hunting and gathering for a life of farming, urbanism and paperwork, and explores why societies became more unequal and hierarchical, including the role war and religion played in such transformations.
    The answers are … More

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    in Humans

    The civilisation myth: How new discoveries are rewriting human history

    Coke Navarro
    FOR almost all of human existence, our species has been roaming the planet, living in small groups, hunting and gathering, moving to new areas when the climate was favourable, retreating when it turned nasty. For hundreds of thousands of years, our ancestors used fire to cook and warm themselves. They made tools, shelters, clothing and jewellery – although their possessions were limited to what they could carry. They occasionally came across other hominins, like Neanderthals, and sometimes had sex with them. Across vast swathes of time, history played out, unrecorded.
    Then, about 10,000 years ago, everything began to change.
    In a few places, people started growing crops. They spent more time in the same spot. They built villages and towns. Various unsung geniuses invented writing, money, the wheel and gunpowder. Within just a few thousand years – the blink of an eye in evolutionary time – cities, empires and factories mushroomed all over the world. Today, Earth is surrounded by orbiting satellites and criss-crossed by internet cables. Nothing else like this has ever happened.
    Archaeologists and anthropologists have sought to explain why this rapid and extraordinary transformation occurred. Their most prevalent narrative describes a sort of trap: once people started farming, there was no way back from a cascade of increasing social complexity that led inexorably to hierarchy, inequality and environmental destruction. This bleak view of civilisation’s rise has long held sway. However, the more societies we look at, the more it falls to pieces. Confronted with inconvenient evidence, we are being forced to retell our own origin story. In doing so, we are also rethinking what a society can be.
    Our … More

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    in Humans

    The societies proving that inequality and patriarchy aren’t inevitable

    The people of Easter Island have shown that systems of governance aren’t set in stoneGetty Images/iStockphoto
    Emerging evidence from the study of human societies past and present reveals a “staggering kaleidoscope of social experimentation”, says David Wengrow at University College London. It is tempting to fit societies into neat categories such as hunter-gatherer versus complex, egalitarian versus hierarchical and democratic versus authoritarian. It turns out to be not that simple. What’s more, a society can change drastically if its members choose.
    One such transition took place on Rapa Nui, also known as Easter Island, in the south-east Pacific. The first settlers established sub-chiefs, each with power over one region of the island and all subordinate to an overall chief. “The chief would have been hereditary,” says Jennifer Kahn at the College of William & Mary in Virginia. “It’s an ascribed position like a monarchy, where you are born into gaining that title.” However, this centralised system proved unstable, so around 1600 the people of Rapa Nui overturned it. In its place they established a birdman cult. Every year, warriors competed by swimming through shark-infested waters to a small islet where they collected a bird’s egg and swam back. “The first one that arrives with their egg unbroken becomes chief for the year,” says Kahn. “It’s an achieved position… that warrior could even be somebody from a low rank.”
    … More

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    in Space & Astronomy

    Julian Muñoz has a ‘ruler’ that could size up the early universe

    Julian Muñoz has come up with a ruler to measure the early universe.

    A theoretical physicist, Muñoz studies the distant, dim period in the universe’s history known as cosmic dawn. That’s when stars first began flickering on, a few hundred million years after the Big Bang, infusing the universe with initial glimmers of starlight and forming the first galaxies.

    Before the first stars, the universe was cold and dark — as Muñoz describes it, “boring.” Then, starlight began to reshape the universe. “It is a very dramatic epoch,” says Muñoz, of the University of Texas at Austin.

    That epoch is also poorly understood. Cosmic dawn is so unexplored that Muñoz compares it to an uncharted area on early maps of Earth. There, Muñoz says, “there could be dragons.” By studying this era, he hopes to reveal the behavior of one dragon of the cosmos, dark matter, the inscrutable substance whose mass binds galaxies.

    But to understand the cosmos, scientists have to be able to measure it. Looking far into space means looking deep into the past. The trouble is our 2-D view of the sky doesn’t readily reveal how far away things are. “When we look at the night sky, we’ve got no depth perception,” says cosmologist Adrian Liu of McGill University in Montreal.

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    Scientists have devised a variety of methods to get a handle on distances, including standard candles and standard rulers — objects of known brightness or length. If you know how bright an object is (compared with how bright it appears) or you know how long a particular feature is on the sky (compared with its apparent length), you can tell how far away it is. A ruler looks smaller from 20 meters away than from 10 meters away, and a 20-watt lightbulb looks dimmer the farther away it is. The same applies over cosmic distances.

    Scientists use certain types of exploding stars, for example, to estimate distances, because the blasts put out a predictable light show (SN: 5/8/12). Standard rulers or standard candles can be used to trace out how far away other objects of interest are and reveal how rapidly the universe has expanded over its history.

    But none of the known standard objects reach back to the cosmic dawn era. That’s where Muñoz’s ruler comes in. “This ability to reach that far back,” Liu says, “that’s the really valuable thing.”

    Sizing up cosmic dawn

    No one has ever seen a conclusive signature of cosmic dawn — the very first galaxies are too distant to observe directly. But there’s another way to spot cosmic dawn’s effects, one that’s been a long-sought target for astronomers. As the first stars formed, their light heated the surrounding hydrogen gas, causing it to absorb light with a wavelength of 21 centimeters, a number that results from the separation between energy levels in hydrogen atoms. Observing that 21-centimeter absorption signal is the aim of the Hydrogen Epoch of Reionization Array, or HERA, collaboration, an effort that Muñoz and Liu both work on, using a radio telescope in South Africa.

    If it can be detected, this absorption signal should have subtle, ring-shaped patterns imprinted in it, Muñoz reported in 2019 in Physical Review Letters.

    Secrets of the universe’s cosmic dawn era are revealed in patterns of the absorption of light with a 21-centimeter wavelength, shown in a computer simulation. Regions with more absorption (red) correspond to denser pockets of stars, compared with sparsely populated regions with less absorption (blue). Sparse areas tend to be separated by distances of about half a billion light-years (arrow indicates one example); the same goes for dense areas.J.B. Muñoz

    Those patterns, the basis of his ruler, result from the differing behavior of dark matter and normal matter during an even earlier period, less than 400,000 years after the Big Bang. Sound waves careening through the plasma at that time would have pushed normal matter to high speeds while leaving dark matter at a standstill.

    This mismatch in velocities affected where galaxies formed during the later cosmic dawn era. To create a galaxy, dark matter must gravitationally reel in normal matter. But where the velocities differed, the normal matter zipped right on by. The early universe was left with sparsely populated regions of the sky, arranged in ring-shaped patterns with a predictable distance scale. The rings, which are too subtle to pick out by eye from the data but show up in statistical analyses, have radii of half a billion light-years – that’s one long measuring stick.

    The new standard ruler could reveal how fast the universe was expanding back then. That information can tell scientists what that youthful universe was made of, revealing the amount of dark matter, normal matter and dark energy, another hidden piece of the cosmic puzzle.

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    A new expansion measurement could also add fuel to one of the fiercest debates in cosmology. Currently, different measurements of the universe’s expansion rate clash with one another, leaving scientists pondering whether there are flaws in our understanding of the cosmos.

    Seeking to understand the unknown, including these shadowy cosmic realms, is “an integral component of human nature — like art and poetry,” Muñoz says. “You could live without it, but I really hope you don’t have to.”

    Looking into dark corners

    Muñoz’s interest in dark matter drew him to the cosmic dawn. The first galaxies grew off a scaffold of dark matter. So information about how and when those galaxies formed can reveal dark matter’s properties. In a report published in 2018 in Nature, for example, Muñoz and colleagues suggested that, if some of the universe’s dark matter had a tiny electric charge, a millionth of an electron’s, that could alter the expected cosmic dawn signal.

    He has also developed important computational tools, like a new technique that allows for lightning-fast simulations of the cosmic dawn, reported in May in Monthly Notices of the Royal Astronomical Society. The time it takes to perform these simulations has previously limited what scientists can study.

    “He’s got an eye for interesting ideas,” says theoretical physicist Marc Kamionkowski of Johns Hopkins University, Muñoz’s Ph.D. adviser. But the cosmic ruler, “that’s probably the most singular idea that he’s had.”

    Becoming a physicist, in itself, was uncharted territory for Muñoz. As a child, he liked science. He recalls being amazed by fossilized shark teeth that were millions of years old — perhaps his first experience grappling with such grand timescales.

    But Muñoz didn’t have a scientific role model; his parents didn’t finish high school. He focused his attention on video games and coding until a high school physics teacher encouraged his scientific streak. He turned to physics, he says, where “it was possible to channel all this nerdy energy for knowledge.” That’s what drives Muñoz to explore the questions that swirl around dark corners of the cosmos. “I do it because I think the answers enrich the human experience.”

    Julian Muñoz is one of this year’s SN 10: Scientists to Watch, our list of 10 early and mid-career scientists who are making extraordinary contributions to their field. We’ll be rolling out the full list throughout 2023.

    Want to nominate someone for the SN 10? Send their name, affiliation and a few sentences about them and their work to sn10@sciencenews.org. More

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    in Space & Astronomy

    A star cluster in the Milky Way appears to be as old as the universe

    One of the oldest known objects in the universe is wandering around the Milky Way.

    Star cluster M92, a densely packed ball of stars roughly 27,000 light-years from Earth, is about 13.8 billion years old, researchers report in a paper submitted June 3 to arXiv.org. The newly refined age estimate makes this clump of stars nearly the same age as the universe.

    Refining the ages of clusters like M92 can help put limits on the age of the universe itself. It can also help solve cosmic conundrums about how the universe evolved.

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    The age is “on the edge of the age of the universe, as estimated by other groups,” says astronomer Martin Ying of Dartmouth College. “It helps us set the lower bound of the age of the universe. We don’t expect M92 to be born before the universe, right?”

    Globular clusters like M92 are tight knots of stars that are thought to have all formed at the same time. That makes it easier for astronomers to measure the stars’ ages (SN: 7/23/21). Stars that are born at different masses have different fates: The big ones use up their fuel quickly and die young, and the small ones linger. Figuring out how many of the cluster’s stars have aged out of the main parts of their fuel-burning years gives a sense of when the whole cluster was born.

    But those estimates rely on assumptions about how stellar evolution works. Ying and colleagues wanted to find an age measurement that would sidestep those assumptions.

    Using a computer, the team created 20,000 synthetic stellar populations for M92, each for a different possible cluster age. They then compared the colors and brightnesses for each of these populations with Hubble Space Telescope observations of M92 and calculated the age that fit the collection best.

    This isn’t the first time astronomers have measured M92’s age, but previous estimates relied on just one synthetic collection of stars. Comparing thousands of them reduced the uncertainty introduced by the assumptions baked into each one. The new technique reduced the uncertainty of the cluster age by about 50 percent, Ying says. The team found the cluster is 13.8 billion years old, give or take 750 million years. That’s strikingly close to the best estimate of the age of the universe: a smidge over 13.8 billion years, plus or minus 24 million years, according to the Planck satellite’s measurement of the first light emitted after the Big Bang (SN: 12/20/13).

    The age of clusters like M92 is important partly because of a rising tension over how fast the universe is growing. Astronomers have known since the 1990s that the universe is expanding at an ever-increasing rate, thanks to a mysterious substance dubbed dark energy (SN: 8/25/22). But recent measurements of the rate of that expansion, a figure called the Hubble constant, disagree with each other (SN: 7/30/19).

    One way around that tension is to accept a different age for the universe, says cosmologist and study coauthor Mike Boylan-Kolchin of the University of Texas at Austin.

    “We often think about it as, Moses came down from Mount Sinai with ‘13.8 billion years’ written on some tablets or something, but it’s not quite like that,” he says. “If one takes the Hubble tension seriously, then one also has to say we don’t know the age of the universe that well.”

    That’s where M92 comes in. Before spacecraft measured the cosmos’ earliest light, globular cluster ages were the best way to place limits on the age of the universe. That practice had fallen out of fashion for a while, says cosmologist Wendy Freedman of the University of Chicago, who was not involved in the new work.

    But improvements in computing, theory, and measurements of the distances to clusters like M92 make it worth trying again.

    “The Hubble tension itself is a really challenging nut to crack,” Freedman says. This measurement alone isn’t precise enough to settle the debate. But “the more kinds of constraints we have, the better,” she says. “It’s showing a way for the future.” More